Hello everybody,I'm trying to research any differences between harnesses of a 2004 2wd 4.3l blazer base model with a/c and my 2001 crew cab with of course 4wd, cruise, and a/c. My current engine is in pretty bad shape and pretty sure the car lot my wife bought it from got a used engine from a salvage yard with all the zip ties holding wiring in place. My buddy had a wreck in his 04 blazer but motor survived. It runs really strong and hasn't had any check engine lights prior to the wreck. I know his motor doesn't have egr or secondary air and discovered the other day that the O2 sensor plugs are different, the knock sensor is different, as well as PCM number. My hopes are to use the motor, harness, and PCM in my truck after having my vin flashed into PCM. I found wiring diagrams for the 2004 online but haven't had any luck on diagrams for my truck to compare against the 04. Can anybody think of anything else that is or might be different between the two?

Quite a few differences in the fuel system and emissions on the 2004 engine.Easiest answer might be to use your sensors, intake and exhaust on the 2004 engine? Basically just use the 2004 long block. Retain all your stock wiring , PCM and BCM.

"Speed doesn't kill, suddenly becoming stationary does." - Richard Hammond"Speed is just a matter of Money - How fast do YOU want to go?"-Mechanic from Mad Max-If at first you don't succeed - Don't take up Skydiving! - ThunderIIKE7CSK

That sucks I was hoping it wasn't going to be more than connecting the 04 harness to the trucks harness and having my vin inputted into the 04 computer. Drilling and threading the engine block for the 01 knock sensor to fit does not sound fun.

Drilling and tapping would not be a plan in my book. Either use an available location, or look for a better transplant option.As much trouble as you are going to put a 2004 V-6 in there you could install a V-8

"Speed doesn't kill, suddenly becoming stationary does." - Richard Hammond"Speed is just a matter of Money - How fast do YOU want to go?"-Mechanic from Mad Max-If at first you don't succeed - Don't take up Skydiving! - ThunderIIKE7CSK

From what I've figured out is besides the hole in the block for the knock sensor being to small for for 2001 knock sensor and a "improved design" timing chain that all my intake and such will swap over. I would love to do a v8 swap but living in California means I could only swap in a 2001 or 2002 light duty van engine or a LSX and the LSX is not gonna be a easy swap following our smog laws. I've done TPI v8 swaps in the old square body s-10's and was fairly easy to follow the swap rules with those and be legal. I just wish I could do what the smog referee calls a smog upgrade and switch to the 2004 setup and get rid of the problematic secondary air crap and digital egr. Can't wait until retirement and escape California and find a state that uses common sense in their engine swap rules.

after 2002 the 2003-2004 electronics were a bit different. you would either have to make the old stuff work on the newer engine or repin/swap your truck over to the newer components from the 2004 truck which might actually be easier if you already have the newer PCM etc. If you find a BCM from a 2004 with 4x4 you can just swap it out and do the passlock relearn and it should work i think.

I would remove all of the wire harnesses and modules from your buddys wrecked truck and go from there. im sure there is a way to do it.